Influence of aging on cortical and trabecular bone response to estradiol treatment in ovariectomized rats

Three groups (n = 15/group) of 6-, 12- and 30-month-old (mature, old and senescent animals, respectively) female Wistar rats on a diet (6 g/100 g BW/ day) containing 0.8% calcium and 0.8% inorganic phosphorus were studied. Within each group, 10 rats were ovariectomized surgically and 5 injected s.c. with 17 beta-estradiol (E rats, 10 micrograms/kg BW/48 h) and 5 with solvent alone (OVX rats) from day 2 until day 60 after ovariectomy. Five other rats were sham-operated (SH rats) and received solvent only. All rats were killed by exsanguination 60 days after ovariectomy. Neither ovariectomy nor estradiol treatment had a significant effect upon tibial mechanical properties in 6-, 12- and 30-month-old animals. Bone mineral density (BMD) and bone mineral content (BMC) of the distal femur and BMC of the whole femur were decreased by ovariectomy in 6- and 12-month-old rats, but were not different in the SH and E groups. In senescent animals, in which the lowest BMD and BMC were measured, estradiol treatment was more effective in increasing these parameters than in adult and old rats. Image analysis of the distal femoral diaphysis showed that estradiol treatment prevented trabecular bone loss induced by senescence and/or ovariectomy. In each group, urinary deoxypyridinoline excretion and plasma osteocalcin concentration were higher in the OVX animals than in the controls, consistent with increased bone turnover in the estrogen-deficient state. Both biochemical turnover markers were reduced in the estrogen-treated groups. These results indicate that 17 beta-estradiol is particularly effective at preventing high-turnover-induced osteopenia in 30-month-old animals.     

Influence of ovariectomy on bone metabolism in very old rats

Twenty-five 30-month-old Lou rats fed a diet (6 g/100 g BW/day) containing 0.9% Ca and 0.8% Pi were divided into five groups. Four groups were surgically ovariectomized. From day 2 until day 29 after ovariectomy, they were S.C. injected either with 17 beta estradiol (E2; 10 micrograms/kg BW/48 hours) or progesterone (P; 140 micrograms/kg BW/48 hours), or 17 beta estradiol + progesterone (E2P) at the same doses, or solvent alone (OVX). The fifth group was sham operated (SH) and injected with solvent. Urine was collected in metabolic cages from day 24 to 29 after ovx, and urinary pyridinoline (PYD) and deoxypyridinoline (DPD) excretion (markers of bone resorption) was measured by HPLC. All animals were killed 30 days after ovariectomy. Serum was then collected for measurement of osteocalcin (OC), alkaline phosphatase (ALP), parathyroid hormone (PTH), and calcitonin (CT). At necropsy, the success of ovariectomy was checked by marked atrophy of the uterine horns. Left and right femur were harvested for densitometric and mineral analysis, respectively. Ovariectomy had no significant effect upon plasma calcium and PTH concentrations. E2 or E2P treatment significantly increased plasma PTH and calcitonin concentrations. Plasma OC concentrations and ALP were not different in any of the groups. In contrast, urinary excretion of PYD and DPD was higher in OVX than in SH rats. Bone mineral density (BMD) of the distal femur was decreased by OVX, but was not different in the E2P and SH groups. A similar pattern was observed for the mineral or Ca content of whole femur. Thus, OVX decreased BMD and bone mineral content (BMC) in very old female rats. Plasma OC concentration and ALP activity failed to demonstrate any significant effect of OVX, whereas PYD and DPD were elevated. These results suggest that bone resorption is increased in OVX rats, even when supplemented with E2 or P alone. However, no significant difference was observed between SH and OVX rats treated with supplementation of both E2 and P. Thus, in very old rats, a combination of E2 and P is much more effective than E2 or P alone to prevent bone loss following ovariectomy.     

Effectiveness of estradiol in preventing and reversing obesity induced by ovariectomy and high-caloric diet in female rats.

Four experiments with 77 female Holtzman rats examined the effects of estradiol benzoate (EB) on food intake, body weight (BW), ano-nasal length, and BW/body length ratio in ovariectomized (OVX) and intact Ss maintained on control or high-fat diets and of OVX and intact Ss that had been reduced by deprivation. EB was highly effective in preventing the increase in food intake, BW, and ano-nasal growth after OVX; it was relatively ineffective in reversing BW gain after OVX. However, when ano-nasal length was also considered, BW was effective in returning OVX Ss to an appropriate BW for their increased ano-nasal length. Intact Ss fed a high-caloric diet did not exhibit an increased rate of ano-nasal growth, which indicates that the skeletal growth that occurred after OVX was not simply a result of increased food intake. It is concluded that EB modulates food intake and BW by multiple mechanisms, one of which is by modulating skeletal growth. The nature of the effect of EB on BW of intact Ss suggests that this effect occurs by still another mechanism. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanism of intracellular calcium homeostasis in heat-exposed cardiomyocytes of rats

The activity of Ca(2+)-ATPase and calcium content were measured in sarcoplasmic reticulum (SR) and mitochrondria of myocardium from 40 adult female Wistar rats after exposure to 37 degrees C, 39 degrees C, 41 degrees C and 43 degrees C for 40 min respectively in vitro. The 45Ca uptake, intracellular free Ca2+ concentration ([Ca2+]i) and the relatively active calmodulin content were also observed in cultured cardiomyocytes from 120 neonatal Wistar rats under the same condition of heat exposure. The results showed that (1) the activity of Ca(2+)-ATPase of SR and mitochrondria of myocardium decreased after heat exposure, (2) the calcium content of SR and mitochrondria also showed a tendency of decrease with increase of exposure temperature, (3) the 45Ca uptake and mean [Ca2+]i increased, whereas the calmodulin content decreased. It is suggested that disturbances of intracellular calcium homeostasis may be responsible for cardiac functional disorder after heat exposure.     

Effects of ovariectomy, 192 IgG-saporin-induced cortical cholinergic deafferentation, and administration of estradiol on sustained attention performance in rats.

Female ovariectomized (OVX) and sham-OVX rats were trained in a task designed to assess sustained attention. After achieving asymptotic performance, OVX rats did not exhibit the impairment in performance over blocks of trials (i.e., the vigilance decrement) observed in sham-OVX rats. Furthermore, OVX rats' performance over blocks of trials was unaffected by the normally detrimental effects of a visual distractor. 192 IgG-saporin-induced lesions of basal forebrain cholinergic neurons resulted in similar impairments in the performance of OVX and sham-OVX rats. The acute, but not chronic, administration of 17β-estradiol attenuated the lesion-induced decrease in the relative number of hits to longest signals exclusively in rats with intact ovaries. These findings indicate that the variables contributing to the potential therapeutic effects of estradiol remain poorly understood. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

钢液成分对钙处理夹杂物改性效果的影响

钙处理是解决铝镇静钢水口结瘤问题的常用手段。通过热力学计算和工业试验研究了钢液成分对钙处理夹杂物改性效果的影响。FactSage热力学计算表明,在一定温度下,钙处理夹杂物改性效果与钢液中氧、硫相对含量密切相关。氧含量一定时,一定范围内的硫含量越高,平衡时夹杂物能达到的最大液相率越小,喂钙量的工艺窗口越窄;硫含量一定时,一定范围内的氧含量越高,平衡时夹杂物能达到的最大液相率越大。工业试验中,对中间包取样,低氧高硫炉次钢中典型夹杂物主要相是高熔点镁铝尖晶石和CaS复合夹杂物,高氧低硫炉次钢中典型夹杂物主要相是低熔点钙铝酸盐。工业试验分析结果与理论计算的趋势一致。     

The effect of estradiol on carbohydrate utilization during prolonged exercise in rats

Female--castrated and male-sham operated rats were subjected to five hours of swimming. It was found that estradiol administered to female rats promotes a supercompensatory pattern of glycogen recovery in the myocardium at the end of the fifth hour of exercise. The hormone markedly delayed the glycogen mobilization from the liver during the first hour of swimming. Glycogen level in m. biceps femoris was essentially unchanged by estradiol both at rest and during exercise. Estradiol signifcantly increased glycogen level in m. masseter of resting rats. Hypoglycaemia developing at the end of the fifth hour of exercise was less pronounced in the estradiol--treated female rats than in the animals from other groups. It may be concluded that estradiol exerts a "sparing" effect on carbohydrate reserves during exercise in rats.     

Increased calcium buffering in basal forebrain neurons during aging

Increased calcium buffering in basal forebrain neurons during aging. J. Neurophysiol. 80: 350-364, 1998. Alterations of neuronal calcium (Ca2+) homeostasis are thought to underlie many age-related changes in the nervous system. Basal forebrain neurons are susceptible to changes associated with aging and to related dysfunctions such as Alzheimer's disease. It recently was shown that neurons from the medial septum and nucleus of the diagonal band (MS/nDB) of aged (24-27 mo) F344 rats have an increased current influx through voltage-gated Ca2+ channels (VGCCs) relative to those of young (1-4. 5 mo) rats. Possible age-related changes in Ca2+ buffering in these neurons have been investigated using conventional whole cell and perforated-patch voltage clamp combined with fura-2 microfluorimetric techniques. Basal intracellular Ca2+ concentrations ([Ca2+]i), Ca2+ influx, Ca2+ transients (Delta[Ca2+]i), and time course of Delta[Ca2+]i were quantitated, and rapid Ca2+ buffering values were calculated in MS/nDB neurons from young and aged rats. The involvement of the smooth endoplasmic reticulum (SER) was examined with the SER Ca2+ uptake blocker, thapsigargin. An age-related increase in rapid Ca2+ buffering and Delta[Ca2+]i time course was observed, although basal [Ca2+]i was unchanged with age. The SER and endogenous diffusible buffering mechanisms were found to have roles in Ca2+ buffering, but they did not mediate the age-related changes. These findings suggest a model in which some aging central neurons could compensate for increased Ca2+ influx with greater Ca2+ buffering.     

Thermal homeostasis in pregnant rats during heat stress.

Sprague-Dawley rats exposed to inescapable heat stress maintained a controlled hyperthermia while increasing heat loss by cutaneous vasodilatation and by grooming behavior. In nonpregnant Ss, the evaporation of saliva groomed onto the body surfaces increased exponentially as a function of ambient temperature above 36°C. In contrast, Ss in an advanced stage of pregnancy became dependent on grooming behavior for thermoregulation of ambient temperatures of 30-36°C. This was associated with a decrease in the body temperature threshold for salivary secretion from the submaxillary gland, which then began at approximately the same body temperature as cutaneous vasodilatation. The pregnant Ss maintained a lower level of controlled hyperthermia during heat stress than did nonpregnant Ss. This appeared to result from a decreased production of metabolic heat, reduced insulation on the ventral surface, and an increased motivation to keep cool during heat stress. These changes met the increased need for thermolysis during pregnancy and provided for thermal homeostasis both in the pregnant rat and in the unborn fetuses. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of fat intake and caloric restriction on bone in aging male rats

Caloric and fat intake may have important skeletal consequences. To evaluate this possibility, skeletal effects of adult-onset caloric restriction (CR) at differing fat intakes were assessed in male Lobund-Wistar rats. At age 17 months, two groups of animals received an anti-obesity diet, restricted approximately 35% from individual ad libitum baseline calorie consumption, and two groups received a diet approximately 50% restricted. Dietary fat concentrations were 5, 15, 15, and 25% by weight, respectively. At ages 20, 24, 28, 30, and 32 months, ex vivo femoral bone densitometry and serum biochemical analyses were performed. Body weight (BW) decreased with time on CR in each group (p < .005), declining faster at the more severe restriction (p = .001). Femoral bone mineral contents (BMC) were also reduced. After adjusting for bone area and BW differences among groups, the only significant difference was a reduction in distal femur BMC in the 25% fat group subjected to more severe CR (p = .02). No differences were observed in serum parathyroid hormone, calcium, phosphorus, or creatinine. Femoral bone loss occurred with CR. This was entirely accounted for by reduction in BW. Higher dietary fat content did not affect BW in CR animals, but did result in lower distal femur BMC.     

Differential modulation of synaptic transmission by calcium chelators in young and aged hippocampal CA1 neurons: evidence for altered calcium homeostasis in aging

The effects of membrane-permeant Ca2+ chelators on field EPSPs (fEPSPs) were measured in the hippocampal CA1 region of brain slices from young (2-4 months) and old (24-27 months) Fischer 344 rats. BAPTA-AM depressed fEPSPs in young slices by up to 70% but enhanced fEPSPs by 30% in aged slices. EGTA-AM, with slower binding kinetics, did not affect fEPSPs from young slices but enhanced fEPSPs in aged slices. BAPTA derivatives with calcium dissociation constants (Kd) of 0.2-3.5 microM reduced or enhanced fEPSPs in young and aged slices, respectively, but 5',5'-dinitro BAPTA-AM (Kd of approximately 7000 microM) had no effect. Frequency facilitation of the fEPSPs occurred in young, but not in aged, slices, except when BAPTA-AM or EGTA-AM was perfused onto aged slices. The differential effects of BAPTA-AM in young and old slices were eliminated by perfusing with a low Ca2+-high Mg2+ saline or with the calcium blocker Co2+. These data suggest that intracellular Ca2+ regulation is altered and raised in aged neurons. Cell-permeant calcium buffers may be able to "ameliorate" deficits in synaptic transmission in the aged brain.     

Thyroxine treatment reduces the anorectic effect of estradiol in rats.

Examined a possible interaction between thyroxine and estradiol in the control of feeding in female Sprague-Dawley rats. 14 ovariectomized Ss were given daily injections of 9.8 μg/100 g of body weight of 1-thyroxine (TX). Another 14 Ss received 0.15 ml of saline (SAL) subcutaneously each day, and food intake was measured for both groups daily. After 15 days of treatment, 8 Ss from each group were also given a single injection of 6 μg of estradiol benzoate (EB), and the remaining 6 Ss of each group received peanut oil vehicle. It was found that TX-treated Ss showed a significantly smaller drop in food intake after EB than did SAL-treated Ss. This TX-induced decrease in responsiveness to EB may be related to effects of TX on general metabolism. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intracellular calcium, DNase activity and myocyte apoptosis in aging Fischer 344 rats

Myocyte apoptosis increases with age in Fischer 344 rats, but the multiple molecular events implicated in this phenomenon remain to be identified. Several defects involving Ca2+ homeostasis, pH, and the expression of p53 and genes of the Bcl-2 protein family may contribute to the activation of myocyte death. Therefore, changes in intracellular pH, cytosolic Ca2+, DNase I and DNase II were measured in myocytes isolated by enzymatic digestion from rats of different ages. Moreover, the expression of p53, Bcl-2 and Bax in these cells was determined. Measurements of intracellular pH by BCECF fluorescence at 3, 12 and 24 months showed that this parameter did not change with age: 3 months, 7.20+/-0.05; 12 months, 7.21+/-0.07; 24 months, 7.18+/-0.09. In contrast, diastolic Ca2+ determined by the Fura 2-AM method increased progressively from 99.8+/-1.9 nm at 3 months to 136.3+/-9.6 nm at 24 months (P<0.001). Concurrently, DNase I activity evaluated by plasmid digestion assay in myocytes increased 3.2-fold from 3 to 24 months (P<0.02). Conversely, pH-dependent-DNase II remained essentially constant with age. Western blotting performed on ventricular myocytes did not detect significant changes in p53, Bax and Bcl-2 proteins with age. Similarly, immunocytochemically, the fraction of myocytes labeled by p53, Bax and Bcl-2 did not change from 3 to 24 months. In conclusion, myocyte aging is characterized by an increase in diastolic calcium which may activate DNase I triggering apoptosis, independently from the expression of p53, Bax and Bcl-2 in the cells.     

Effects of chronic nimodipine on working memory of old rats in relation to defects in synaptosomal calcium homeostasis

The present study was designed to investigate whether chronic (from 12 to 23 months of age) dietary treatment with the L-type Ca2+ channel blocker nimodipine (30 mg/kg body weight) enhances the cognitive behavior of aged animals and whether such a treatment would have long-term effects on the mechanisms of Ca2+ regulation in synaptic terminals from the aged rat brain. Cognitive behavior was evaluated in an 8-arm radial maze in 6 test series comprising a total of 105 test sessions, with intervals of no training between series. Nimodipine-treated rats performed better than vehicle-treated, aged-matched controls in all the test series, making more correct choices every time a new series was initiated. However, differences between nimodipine- and vehicle-treated rats were most remarkable in the last three test series, when the rats were 19 to 22 months. In these series 74% of the nimodipine-treated rats were able to perform the task in 4 to 9 test sessions whereas only 12%, 14% or none of the control rats learned the task. To study Ca2+ regulation in synaptosomes derived from cerebral cortex and hippocampus, we analyzed 45Ca2+ accumulation as well as the levels of the Ca2+-binding proteins calbindin-D28K and calreticulin by Western blotting. Nimodipine administration had no effect on hippocampal synaptosomes but increased the levels of calbindin-D28K and calreticulin in cerebral cortex preparations. These results indicate that chronic nimodipine treatment from 12 to 23 months of age prevents age-induced learning deficits without showing any signs of toxicity, and that these effects are associated with a small increase in the levels of synaptosomal Ca2+-binding proteins from cerebral cortex. The up-regulation of these proteins might provide a link between the long-term effects of nimodipine on gene expression and learning ability in old rats.     

Study of calcium homeostasis in feline hyperthyroidism

Thirty cats with untreated hyperthyroidism were blood sampled and their calcium homeostatic mechanisms and renal function assessed. The results were compared with those obtained from 38 age-matched control cats. The hyperthyroid group of cats were found to have significantly lower blood ionised calcium and plasma creatinine concentrations and significantly higher plasma phosphate and parathyroid hormone concentrations. Hyperparathyroidism occurred in 77 per cent of hyperthyroid cats, with parathyroid hormone concentrations reaching up to 19 times the upper limit of the normal range. The aetiology, significance and reversibility of hyperparathyroidism in feline hyperthyroidism remains to be established but could have important implications for both bone strength and renal function.     

Effect of thapsigargin on calcium homeostasis in Trypanosoma cruzi trypomastigotes and epimastigotes

By using the fluorescent calcium indicator fura-2, it was found that the concentration of free Ca2+ in the cytoplasm of Trypanosoma cruzi trypomastigotes incubated in the presence or absence of external calcium was maintained at very low levels (10-20 nM). When trypomastigotes were incubated in the presence of succinate and ATP and permeabilized with digitonin, they lowered the medium calcium concentration to a submicromolar level. In the presence of 1 microM FCCP the initial rate of Ca2+ sequestration by these permeabilized cells was very slow. When succinate alone was present, the initial rate of Ca2+ accumulation was slower than with ATP plus succinate, and the calcium set point was about 0.6 microM. The succinate dependence and FCCP sensitivity of the later Ca2+ uptake indicate that it may be exerted by the mitochondria. High concentrations of the tumor promoter thapsigargin slightly increased cytosolic Ca2+ in the presence of extracellular Ca2+ but had no effect on the FCCP- and oligomycin/antimycin A-insensitive Ca2+ pool. In addition, when used at those concentrations (4-20 microM), thapsigargin was shown to release Ca2+ from the mitochondria and to decrease the inner mitochondrial membrane potential of trypomastigotes and epimastigotes as measured using safranine O. Despite the presence of inositol phosphates as determined by [3H]inositol incorporation, no IP3-sensitive Ca2+ release could be detected in trypomastigotes.     

The regulation of calcium homeostasis in nerve cells

We have reviewed the major cellular elements related to the release and buffering of calcium in neurons. Voltage-operated, chemical-operated calcium channels and mechanisms of stability of intercellular calcium homeostasis (mitochondria, endoplasmic reticulum, calcium binding proteins, calcium exchange and calcium pump) are demonstrated in normal and pathological condition (105 ref.).